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  • Publication
    Accès libre
    Use of Cl/Br Ratio to Decipher the Origin of Dissolved Mineral Components in Deep Fluids from the Alps Range and Neighbouring Areas
    (2010)
    Sonney, Romain
    ;
    ;
    Cattin, Stéphane
    Cl/Br ratios were studied in deep groundwaters to decipher the origin of dissolved mineral components from the Alps and neighbouring areas. Cl/Br molar ratio represents a good marker to define if the salinity comes from seawater or residual brines (655 and lower) or from dissolution of halite or halite-rich gypsum, often present in the Triassic formations (upper than the seawater ratio). It can be an interesting tool for projects dealing with exploration and production of geothermal fluids. Results of this study showed the presence of trapped seawater in formations of the large basins from the Quaternary to the basement, resulting from infiltration during different marine intrusion periods. This method also showed the presence of brines in crystalline aquifers. Some of these waters discharge along subvertical faults and are diluted to various degrees by different types of meteoric waters. In some cases, this method raises new questions about the true geological origin of deep circulations.
  • Publication
    Accès libre
    Validation of Chemical and Isotopic Geothermometers from Low Temperature Deep Fluids of Northern Switzerland
    (2010)
    Sonney, Romain
    ;

    During more than 30 years, chemical and isotopic geothermometers have been extensively used to calculate and estimate the temperature of geothermal reservoirs in various geological, petrographical and thermal conditions. In this evaluation, chemical analyses of deep boreholes from the Molasse Basin and the Tabular Jura in Northern Switzerland were used to estimate reservoir temperatures with geothermometers, and results were compared to measured temperatures at depth. The presence of thermal waters in subhorizontal formations with a temperature range of 12-112°C, is associated with various geological and petrographical settings (sedimentary, crystalline rocks).

    Composition of geothermal fluids depends on various and sometimes competing processes, such as full or partial chemical equilibrium, mixing with shallow groundwater or trapped seawater, dissolution of evaporite, ionic exchange with clays, or residence time in the reservoir. These processes are constraining for the application of geothermometers. Moreover, some of them have a limited temperature range of application cannot be used in some petrologic environments. Thus, a range of possible reservoir temperatures is calculated depending on several assumptions and compared to measured temperature. Application of chemical and isotopic geothermometers, using several calibrations proposed in the literature, is discussed in this specific context.
  • Publication
    Accès libre
    The Database of Geothermal Fluids in Switzerland on Google Earth
    (2010)
    Sonney, Romain
    ;
    ;
    Cattin, Stéphane

    The database BDFGeotherm, containing physical, chemical and hydrogeological information on more than 200 deep fluids from 84 sites in Switzerland and some neighbouring regions, was first compiled on ACCESS code and was later modified to improve its availability and attractiveness by using Google Earth free software and the CREGE website (www.crege.ch/BDFGeotherm/). BDFGeotherm is a functional tool for various phases of a geothermal project such as exploration, production or fluid re-injection. This database allows gathering existing geothermal data, generally widely dispersed and often difficult to reach, towards a user’s friendly tool. Downloading the file “BDFGeotherm.kmz” from the CREGE website makes possible to visualize the 84 geothermal sites from Switzerland and neighbouring areas. Each one is represented with a pinpoint of different colour, for diverse temperature ranges.

    A large majority of sites is located in the northern part of the Jura Mountain and in the upper Rhone Valley. General information about water use, geology, flow rate, temperature and mineralization are given in a small window by clicking on the desired pinpoint. Moreover, two links to Internet addresses are available for each site in each window, allowing returning to the CREGE website or providing more details on each sampling point such as: geographical description, reservoir geology, hydraulics, hydrochemistry, isotopes and geothermal parameters. For a limited number of sites, photos and a geological log can be viewed and exported (Sonney et al., 2009).